# How to Calculate Your Body Mass Index (BMI)

Knowing your body mass index, or BMI, can be useful for assessing and adjusting your weight. It is not the most accurate measure of how much body fat you have, but it is the easiest and least expensive way to measure it. There are different ways of calculating your BMI depending on the type of measurements you have taken. Make sure that you know your current height and weight before you get started and then try calculating your BMI.

### Method 1 Using Metric Measurements

1. 1
Take your height in meters and square the number. You will need to multiply your height in meters by itself first. For example, if you are 1.75 meters tall, then you would multiply 1.75 by 1.75 and get a result of approximately 3.06.
2. 2
Divide your weight in kilograms by meters squared. Next, you will need to divide your weight in kilograms by your height in meters squared. For example, if your weight is 75 kilograms and your height in meters squared is 3.06, then you would divide 75 by 3.06 for an answer of 24.5 as your BMI.
3. 3
Use an extended equation if your height is in centimeters. You can still calculate your BMI if your height is in centimeters, but you will need to use a slightly different equation to do so. This equation is your weight in kilograms divided by your height in centimeters, then divided again by your height in centimeters, and then multiplied by 10,000.
• For example, if your weight in kilograms is 60 and your height in centimeters is 152, then you would divide 60 by 152, by 152 (60 / 152 / 152) for an answer of 0.002596. Multiply this number by 10,000 and you get 25.96 or about 30. The approximate BMI for this person would be 30.

### Method 2 Using Imperial Measurements

1. 1
Square your height in inches. To square you height, multiply your height in inches by itself. For example, if you are 70 inches tall, then multiply 70 by 70. Your answer for this example would be 4,900.
2. 2
Divide weight by height. Next, you will need to divide your weight by your squared height. For example, if your weight in pounds is 180, then divide 180 by 4,900. You would get an answer of 0.03673.
3. 3
Multiply that answer by 703. To get your BMI, you will then need to multiply your last answer by 703. For example, 0.03673 multiplied by 703 equals 25.82, so your approximate BMI in this example would be 25.8.

### Method 3 Using a Metric Conversion Factor

1. 1
Multiply your height in inches by 0.025. 0.025 is the metric conversion factor necessary to turn inches into meters. For example, if your height is 60 inches, then you would multiple 60 by 0.025 for an answer of 1.5 meters.
2. 2
Square your last result. Next, you need to multiply the last number you got by itself. For example, if the last number you got was 1.5, then multiple 1.5 by 1.5. In this situation, your answer would be 2.25.
3. 3
Multiply your weight in pounds by 0.45. 0.45 is the metric conversion factor needed to convert pounds into kilograms. This will convert your weight into its metric equivalent. For example, if your weight is 150 pounds, then your answer would be 67.5.
4. 4
Divide the larger number by the smaller number. Take the number you got for your weight and divide it by the number you got for your squared height. For example, 67.5 would need to be divided by 2.25. The answer is your BMI, which in this example would be 30.

### Method 4 When Should You Try This?

1. 1
Calculate your BMI to determine if you are at a healthy weight. Your BMI is important because it can help you to determine if you are under weight, normal weight, over weight, or obese.
• A BMI below 18.5 mans that you are under weight.
• A BMI of 18.6 to 24.9 is healthy.
• A BMI of 25 to 29.9 means that you are overweight.
• A BMI of 30 or greater indicates obesity.
2. 2
Use your BMI to see if you are a candidate for bariatric surgery. In some situations, your BMI may need to be above a certain number if you want to have bariatric surgery. For example, to qualify for bariatric surgery in the UK, you would need to have a BMI of at least 35 if you do not have diabetes and a BMI of at least 30 if you do have diabetes.
3. 3
Track changes in your BMI over time. You can also use your BMI to help you track changes in your weight over time. For example, if you want to chart your weight loss, then calculating your BMI on a regular basis might be helpful. Or, if you want to track growth in yourself or in a child, then calculating and tracking BMI is another way to do that.
4. 4
Calculate BMI before considering more expensive and invasive options. If you can determine that your body weight is in the healthy range using your BMI, then this might be the best option. However, if you are an athlete or an avid sports enthusiast and you think that your BMI is giving an inaccurate picture about your body's fat content, then you might want to consider using a different option.
• Skin fold tests, underwater weighing, dual-energy x-ray absorptiometry (DXA) and bioelectrical impedance are some of the other options available for determining your body's fat content. Just keep in mind that these methods are more expensive and invasive than calculating BMI.

## Tips

• Maintaining a healthy weight is perhaps the single most important step you can take toward optimal health and long life. Calculating your BMI is only a rough indicator of your general condition and physical health.
• Another easy way to determine if you are at a healthy weight is to calculate your waist to hip ratio.

## Warnings

• The BMI is a pretty good indicator for the average person from age 25 to 65. But it has its limitations. It does not take into account muscle mass or your overall body type ("apple" vs. "pear" body types).

## Things You'll Need

• Bathroom scale
• Yardstick or measuring tape
• Pencil and paper
• Calculator

## Article Info

Categories: Diet & Lifestyle